Reticular activating system

The reticular activating system is the name given to the part of the brain (the reticular formation and its connections) believed to be the center of arousal and motivation in animals (including humans).

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Functions

The activity of this system is crucial for maintaining the state of consciousness. It is situated at the core of the brain stem between the myelencephalon (medulla oblongata) and mesencephalon (midbrain).

It is involved with the circadian rhythm; damage can lead to permanent coma. It is thought to be the area affected by many psychotropic drugs. General anaesthetics work through their effect on the reticular formation.

Fibers from the reticular formation are also vital in controlling respiration, cardiac rhythms, and other essential functions.

Although the functioning of this system is a prerequisite for consciousness to occur, it is generally assumed that this system's role is indirect and it does not, by itself, generate consciousness. Instead, its unique anatomical and physiological characteristics ensure that the thalamocortical system fire in such a way that is compatible with conscious experience.

Clinical significance

The reticular activating system has received attention from neuroscientists interested in various pathological conditions affecting behaviour, such as Alzheimer's Disease. More recently, results of research on the area has prompted extrapolations from the data into attention-deficit hyperactivity disorder (ADHD). The reticular activating system is believed to cause ADD and ADHD due to the imbalance of norepinephrine in the cells. This leads to the over-arousal and lack of motivation associated with these disorders. [Needs citation; clarification of "imbalance of norepinephrine" (excess? inadequate?); and explanation of the mechanism by which the RAS is believed to increase arousal while decreasing motivation.] However, despite the recent rapid increase in knowledge of the structure and function of the brain, assumptions about brain function related to real-world events made without specific evidence should be treated with extreme caution.